Week 1 Flashcards
What are the 4 drug targets for antimicrobials?
1) Cell wall synthesis- Pencillin inhibits transpeptidase involved in forming crosslinks between peptidoglycans.
2) Cell membrane function- macromolecules/ions escape leading to cell death.
3) Protein synthesis- Tetracyclin blocks tRNA molecule site on 30S ribosome subunit.
4) Nucleic acid synthesis- Rifampin prevents RNA synthesis.
What are different the different types of antibiotic resistance?
1) Enzymes degrade antibiotic
2) Alteration of target site
3) Bacterial cell impermeable
4) Elimination of antibiotic from bacteria
Name 3 reasons why microbiology is important in vet med?
1) Understanding diseases
2) Recognise emerging diseases
3) Improve control of known infections
Differentiate between fungi. bacteria, viruses and TSE(prions)
Fungi- formed as environmentally resistant spores and moulds.
Bacteria- 10-100 times larger than viruses.
Virus- cannot replicate outside of host cell.
Prion- smaller than virus( causes BSE) and made of alpha coils.
Name 2 genomic and 4 structural elements of bacteria?
Genomic:
1) Chromosome- haploid, circular DNA, compacted into a nucleotide.
2) Plasmid- has partition genes.
Structural:
1) Bacterial cell wall- peptidoglycan protects from osmotic lysis.
2) Capsule- extracellular matrix protects bacteria from drying and provides biofilm matrixes.
3) Flagella- protein tails
4) Pili- for adhesion purposes
State some structural features for the 4 different bacteria groups?
Gram positive- thick peptidoglycan cell walls, take up crystal-violet dye and stained purple.
Gram negative- thin pep cell wall (impermeable), stained pink and have porins.
Acid fast- contain large amounts of glycolipids and resist decolorisation by acid, stain red
Mycoplasma- lack cell wall, appears pleomorphic.
What are ABC transporters?
They use ATP to transport molecules. P-glycoprotein is an example expressed in capillary endothelial cells.
What is the notion of lipid rafts?
Interactions between lipids generate the formation of lipid rafts which are involved in cell signalling. Intracellular signalling molecules and receptors are concentrated in the rafts.
Describe DNA organisation( chromatin + nucleosomes)
DNA is condensed into a chromosome set consisting of linear DNA and Nucleosomes to form chromatin. Each nucleosome is composed of octamer histone proteins( H2A, H2B, H3 and H4) Nucleosomes are separated by linker DNA.
How is genetic info stored in terms of DNA, genes and chromosomes?
Genes consist of exons (coding) and introns (non-coding). They contain start and stop sequences and an open reading frame which determines translation. Genes have short p regions and long q regions.
Describe the composition and structure of ribosomes?
2 subunits: in prokaryotes this is 70S(30 and 50s) and on eukaryotes this is 80S( 40s and 60s.)
Describe the cloverleaf structure and function of tRNAS?
- wobble hypothesis
- 2 critical regions
- 2 chemical reactions
tRNA’s have 2 critical regions: the anticodon and the aa acceptor stem(3’ end). The wobble hypothesis explains how one tRNA molecule can recognise and bind to more than on codon. 2 chemical reactions occur when the aa-tRNA complex forms:
1) adenylation of aa
2) transfer of aa to tRNA
Describe the 3 main steps that occur during polypeptide chain synthesis?
1) Initiation: the ribosome, mRNA and tRNA carrying methione all come together forming the initiation complex.
2) Elongation: aa’s are brought together by tRNAs and are linked to form a chain.
3) Termination: a STOP codon enters the A site and chai is separated from tRNA.
How can polypeptide chain synthesis go wrong?
- The ribosome could start translating in the wrong place.
- Insertion of wrong aa.
- Indel mutations.
- Premature termination.
Why are ribosomes important as an antimicrobial drug target? Tetracyclins?
Eukaryotes and prokaryotes have different size ribosomes. Tetracyclin binds to 30S subunit at A site and prevent attachment of tRNAs to aa’s.
Describe the 3 steps of RNA processing in transcript production:
- RNA 5’ capping
- Addition of RNA 3’ poly A tail
- RNA splicing
RNA 5’ capping: RNA transcripts are capped by addition of 7-methylguanesine which enables stabilisation and protection against exonuclease attack as well as promoting intron excision.
Addition of RNA 3’ poly A tail: a series pf adenosine(50-250) are added to the 3’ end to:
- protect against exonuclease attack
- terminate transcription
- aid in mRNA exportation
RNA splicing: Both exons and introns are transcribed into pre-mRNA and then the introns are removed by splicing in spliceosomes and exons are retained and joined.
Describe 4 major mechanisms for regulating gene expression?
1) Transcription factors- control gene expression by binding to DNA sequence and increasing/decreasing transcription.
2) Epigenetic modification of chromatin- modification of piston details regulates gene expression. Heterochromatin means no transcription occurs, Euchromatin means it does.
3) mRNA stability- stability/destruction regulates GE.
4) Non-coding DNA- miRNA binds to mRNA and it’s degraded and PS is reduced.
What is meant by RNA-alternative splicing?
Different patterns of splicing within the same gene where exons are arranged in a different order.
Describe how you would carry out a spore stain?
1) Stain with malachite green and hold for 3-6 mins over steam/heat.
2) Rinse with water.
3) Counter stain for 30 secs.
4) Rinse under water and dry.
Describe how you would carry out a GRAM stain?
1) Add crystal violet stain and stand for 30-60secs and rinse.
2) Add iodine solution, leave for 30-60 secs and rinse.
3) Add some decolouriser and rinse after 5 secs.
4) Counter stain with carbon- fuchsin(safarin) for 30-60 secs and rinse.
5) Air dry and view.
Name 3 different methods for measuring bacterial growth?
1) Growth in liquids (measure absorbance through cuvette)
2) Direct microscope counting
3) Colony counting( serial dilutions)
Define facultative anaerobe and microaerophilic:
Facultative anaerobe: organism that makes ATP by aerobic respiration if O2 is present but can switch to anaerobic if not.
Microaerophilic: organism that require ver little O2(lower than atmosphere.)
Describe bacterial terms for growth at different pH’s, temperatures and osmolarities?
pH- most media is buffered at around 7, when bacteria grow, they may produce acidic metabolites.
Temperature- psychrophiles are grown below 25 degrees, mesophiles at 37 and thermophiles over 45.
Osmolarity- bacteria prefer to maintain a slight positive pressure.
What are chemotrophs and phototrophs?
Chemotroph- organisms that obtain energy by oxidation of electron donors in their environments.
Phototroph- use light to gain energy
What are some functions of the cytoskeleton?
- Help strengthen cell and maintain shape.
- Responsible for movement of materials within the cell.
- Cause cell to move.
Describe ‘Dynamic instability’ and ‘filament treadmilling’
DI- the assembly and disassembly at microtubule ends. There’s a positive GTP dimer ‘cap’ on one end and a centromer on the negative end.
Treadmilling- positive barbed end grows quicker than the negative pointed end.
What are the differences between cilia and flagella?
Cilia- short, next arm present, rotational and fast moving.
Flagella- long, no next arm present, undulating motion.
How does the cytoskeleton contribute to movement across the substratum?
Surface crawling:
1) Protrusion- actin-rich structures are pushed out in front of cell.
2) Attachment- adhesion to substratum via focal contacts.
3) Traction- generated by myosin motor proteins at rear propels cell forward.
How can the cytoskeleton be exploited in drug development?
Antihelminthic drugs- inhibits tubulin polymerisation.
Chemotherapy- Vincristine binds to tubular dimers causing disassembly of microtubule structures. Paclitaxel prevents microtubules from losing subunits.
Compare the 2 types of microtubule motor proteins:
Kinesins: travels along microtubule negative to positive end, consists of 2 heads moving in walking like action, driven by ATP hydrolysis, tail binds to cargo.
Dynesins: travels along microtubule towards cell body positive to negative end, largest and fastest MP’s, driven by ATP hydrolysis, beating of c and f.
How do motor proteins generate force by coupling ATP hydrolysis to confrontational changes?
The conformational change on MP prevents next nucleotide binding/hydroysis until prior round of hydrolysis and release is complete. The is the ‘power stroke’ cycle.
